The present invention relates to electrical reactors and, more particularly, to a high current reactor in which current carrying windings are resiliently supported in a magnetizable core.
A reactor comprises one turn or more of an electrical conductor wound in a substantially closed loop. In a so-called iron core reactor the conductor is typically wound on at least one leg of a core of magnetizable material. To reduce heating of the core caused by eddy currents circulating in the core, the core is generally formed as a laminated structure. Under steady state conditions the reactor presents a relatively low impedance to direct current of constant magnitude and a relatively high impedance to alternating or otherwise undulating currents, the impedance varying substantially as a direct function of the frequency of the alternating current. Accordingly, if the winding is connected in series with a source of direct current having an appreciable ripple, its inductance is effective to smooth the current that flows to a connected load circuit. In high current applications (e.g., 1000 amperes or more), such smoothing reactors are typically large devices and can occupy a volume of as much as 70 cubic feet and weigh several tons.
The conductors forming the windings of these high current reactors are typically insulated copper bars of relatively large cross sectional area, e.g., the bars may be one inch wide and one-half inch thick. Windings formed of such conductors are generally wound in flat spiral layers with one end of the conductor terminating at the outer periphery of the layer and the other end of the conductor terminating at the inner periphery of the layer. A plurality of these "winding layers" may be stacked with suitable insulation between each layer to form a complete winding or "coil stack." The conductors may be selectively joined at respective inner and outer end terminals to form any desired combination of winding layers. For example, by connecting all the inner end terminals to a first common point and connecting all the outer end terminals to a second common point, a single reactor coil stack having all winding layers in parallel will be formed.
In order to minimize the size of such reactors, it is necessary to tightly compact the coil stack while at the same time providing adequate electrical insulation between the turns of each winding layer and between adjoining layers in order to prevent arcing or electrical breakdown between adjacent conductors. During operation of the reactor there is a tendency for the winding to more or vibrate due to thermal expansion or contraction, undulations in the magnetic forces exerted on the conductors, and mechanical vibrations of the supporting structure. Relative movement between adjacent winding layers or between individual turns of the winding layers will result in large frictional forces being exerted on the electrical insulation surrounding the conductor. Repetitive frictional forces can eventually result in electrical breakdown of the insulation with attendant arcing and other damage to the reactor and associated components.
Prior art attempts to solve the problem of insulation breakdown due to relative conductor movement have generally involved restricting the movement of the winding layers and turns by applying an external compressive force to the coil stack. Such a prior art construction is shown in U.S. Pat. No. 2,064,011 wherein an expansible closed hollow member is assembled as part of a coil stack in a transformer. After assembly of the coil stack within the transformer housing or outer core structure, a suitable filling compound is forced under pressure into the expansible member thereby forcing the member to expand and compress the coil stack. The filling compound is then allowed to set or harden before using the transformer. Such a construction is disadvantageous in at least two respects: the expansible member is metal which can adversely affect the alternating flux distribution in the device; and, due to the rigidity of the filling compound, when used in a vibrating environment frictional forces will tend to cause insulative spacers in the transformers to wear which can undesirably reduce the compressive forces exerted on the coil stack.
A more recently developed approach to this problem is illustrated in U.S. Pat. No. 3,170,131 wherein the filling compound is a compressible gas. This approach tends to overcome the problems of a solid filler since the gas will expand and compensate, albeit at a lower pressure, for any wear in the insulative spacers within the transformer structure. Although leakage of the gas from the expansible member creates another problem, the latter problem may be alleviated by periodically checking the gas pressure and replacing the gas as required. However, a further problem introduced by this approach is one of lateral support of the coil stack. In particular, the gas fill member under high compressive stress and lateral forces acts much like a balloon filled with air, i.e., it has very little resistance to lateral movement. Furthermore, with the high compressive forces necessary to minimize coil movement, the gas filled member has very low vibration damping ability even in the compressive direction.
As will be fully explained hereinafter, my invention utilizes ripple springs in the reactor assembly. Such ripple springs per se have previously been disclosed. A ripple spring typically comprises a corrugated sheet of alternating rises and valleys uniformly distributed across the surface area of the sheet, the sheet being formed of a stiff but bendable resilient material.